In the area of image reproduction, as the quality of reproduced images increases, the size of toner rendering the high quality images is generally reduced. Since high quality reproduced images usually appear more exact to the original, its reproduction process must reflect the exactness of minute details of the original images. At the above described high resolution, an image reproduction process requires significantly fine toner to faithfully reproduce original images in the exact manner. Because of the size, a larger number of the small toner particles is placed in a unit area than any large toner particles. The larger number of small toner particles allows the more exact rendition of minute details of the original.
In order to render a high quality reproduced image, the above described small toner is preferably spherical in its configuration. As toner is manufactured to reduce its size, the toner generally loses its mobility. The mobility allows toner to settle itself on an applied surface and forms a uniform layer. Because of the lack of this mobility, the irregularly shaped toner lumps together as it is applied on an image forming surface and prevents a smooth and uniform application in a desired area of the image forming surface. As the result of the non-uniform application, a reproduction process cannot yield a desired high resolution image. To preserve the above described mobility on the fine toner, Japanese Patent 6-17373 discloses a method of manufacturing ultra-fine spherical toner.
According to Japanese Patent 6-17373, the method of manufacturing spherical toner particles involves steps of dissolving 0.1-5% weight high polymer in a hydrophilic organic solution, and adding a single vinyl compound in less than 20 times the weight of the above high polymer. The vinyl dissolves in the hydrophilic organic solution, but the yielded vinyl-high polymer compound does not substantially dissolve in the hydrophilic organic solution. The above yielded toner compound averages its size in the range of 1 to 100 microns. In addition, the size distribution of the above yielded toner compound indicates that the above range with its .+-.25% variations amounts to approximately over 95% of the entire size spectrum. Other details regarding the dying procedures in the above described Japanese patent are hereby incorporated by the external reference and constitutes an inessential part of the current application.
The above described mobile ultra-fine spherical toner generally helps reproduce high resolution images but contributes to a difficulty in removing residual toner from the image forming surface during a cleaning procedure. To appreciates the above mentioned difficulty in the cleaning procedure, referring to FIG. 1, a photocopying process is generally described. To photocopy an original image on an image-carrying medium 60, a scanned original image is developed on an image forming surface of a photoreceptor drum 20. To develop the image, a charger 30 forms an uniform layer of electrical charges on the image forming surface 20 prior to a selective removal by exposing a predetermined light according to the scanned original image. The electrically represented original image on the photoreceptor drum 20 is then developed by applying toner contained in a developer 40. Because of the electrical charge, the applied toner is selectively adhering to the photoreceptor drum 20 and is finally transferred to an image-carrying medium 60 via a transfer charger 70. Since the above applied toner is not completely transferred to an image-carrying medium 60, some toner remains on the photoreceptor drum 20. The residual toner must be removed before the next photocopying process so that the residual toner does not undesirably interfere the next reproduction process.
To remove the above described residual toner from the photoreceptor drum 20, a cleaning unit 26 performs a cleaning procedure. Still referring to FIG. 1, the cleaning unit 26 is located near the photoreceptor drum 20 as well as the transfer charger 70 and generally includes a cleaning blade 24 and a cleaning brush 25. After the toner representing an original image is transferred to an image-carrying medium 60, a portion of the toner remaining on the image forming surface is transported towards the cleaning unit 26 as the photoreceptor drum 20 is rotated in a clockwise direction as indicated by an arrow. When the residual toner approaches the cleaning unit 26, the cleaning brush 25 initially removes a certain portion of the residual toner off the photoreceptor drum 20. The removed toner is collected in the cleaning unit housing. However, some portion of the residual toner still remains on the photoreceptor drum 20 and is removed by the cleaning blade 24 as the photoreceptor drum 20 is further rotated. The cleaning blade 24 is generally made of flexible rubber and is positioned so that at least its edge portion is pressed against the rotating photoreceptor drum 20 at a predetermined oblique angle. Because of the above described press fit contact, the residual toner is further removed from the photoreceptor drum surface 20. The removed toner is collected in the cleaning unit housing 26 and is transported by a collection coil 28 for the recycling use. With the use of large conventional toner particles, the above described brush and cleaning blade remove substantially all the residual toner particles and the photoreceptor drum 20 is able to reproduce another image without any interference from the residual toner.
In contrast to the above described effectiveness of the cleaning process against the removal of the conventionally sized toner particles, the conventional cleaning process cannot effectively remove the ultra-fine spherical toner to the same extent. In other words, when the ultra-fine spherical toner is used in the photocopying device as described with respect to FIG. 1, repeated image production outputs undesirable images, for example, with streaks of lines caused by the unremoved residual ultra-fine spherical toner. The reasons for failing to remove the undesirable residual toner are hypothesized, and one of the hypotheses is described in FIGS. 2A-2C.
Referring to FIGS. 2A-2C, the above described undesirable residual toner is not removed by a cleaning blade 24. FIG. 2A diagrammatically illustrates a cross-sectional view of a residual portion of ultra-fine spherical toner 22 remaining on a photoreceptor drum 20 and approaching a cleaning blade 24. When the spherical toner 22 contacts the cleaning blade 24, it rotates on the surface of the photoreceptor drum 20 so as to push the cleaning blade 24 away from the image forming surface for creating a gap. As the photoreceptor drum 20 further rotates as indicated by an arrow, the spherical toner 22 also further rotates and escapes through the gap to the other side of the cleaning blade 24 as shown in FIG. 2C. Thus, the cleaning blade 24 fails to remove the residual spherical toner 22 from the photoreceptor drum 20. In the alternative, although not shown in the above referenced figures, the ultra-fine toner also escapes the cleaning blade pick-up through a gap that exists without the above described push-up motion by the spherical toner. Since either the blade edge or the developing surface is not perfectly smooth, there exist minute gaps between the blade edge and the image forming surface. In fact, the smaller the toner, the more easily it escapes through the above described minute gaps. Consequently, regardless of the blade failure to remove the ultra-fine toner, the undesirably remaining spherical toner will be interfering with the next image production process. Although the conventional photocopying device can potentially improve certain image qualities with the use of the ultra-fine spherical toner, even the normal use of the photocopying device cannot take advantages of the above described favorable features of the ultra-fine spherical toner. To capitalize the advantageous features of the ultra-fine spherical toner, the prior attempts involve various approaches. For example, Japanese Patents 60-12360, 60-12361 and Japanese Patent Open-Laid Publication 60-131547 disclose one approach in which the above described ultra-fine spherical toner is mixed with larger irregularly shaped toner prior to the application onto an image forming surface. Although the cleaning efficiency of a conventional cleaning unit has increased due to the larger irregularly shaped toner, as intuitively clear, the reproduced image quality by the mixed toner has degraded also by the irregularly shaped large toner. Another approach, for example, disclosed by Japanese Patent 4-288554 involves the application of a cleaning enhancing agent onto the residual toner remaining on the photoreceptor drum prior to the blade cleaning. The cleaning enhancing agent includes non-toner particles of 10-30 microns with approximately 0.05-2 weight % of mobility enhancer. To apply the cleaning enhancing agent, an additional container as well as an associated controller for regulating the application of the cleaning enhancer are required. In addition to the additionally required hardware, this approach is also cost prohibitive due to the additional supply of the cleaning enhancing agent. The above described prior attempts cannot fully capitalize the advantages of the ultra-fine spherical toner without additional costs and are desired to be improved.